1. Field of the Invention
The present disclosure relates to a positive electrode composition for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.
2. Description of the Related Art
With the progress in spread and miniaturization of mobile devices such as VTR, mobile phone and note PC, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery has recently been used as a power supply therefore. Furthermore, the non-aqueous electrolyte secondary battery has attracted a great deal of attention as a power battery for electric vehicles and the like so as to cope with environmental problems.
There has widely been employed, as a positive electrode active material for a lithium secondary battery, LiCoO2 (lithium cobalt oxide) that can constitute a 4 V class secondary battery. Cobalt, that is a constituent component of a raw material for LiCoO2, is a scarce resource and is also unevenly distributed, which leads to high costs and causes anxiety about supply of the raw material.
In response to these circumstances, lithium transition metal composite oxides which have a stacked-layer structure such as nickel-cobalt-lithium manganate in which a part of the Co in LiCoO2 is substituted with other metals such as Ni and Mn, have been developed. Generally, in the lithium transition metal composite oxides which have a stacked-layer structure, the greater the content ratio of nickel, more unstable the crystal structure will become, which may result in deposition of lithium compounds in the positive electrode slurry during manufacturing of the positive electrodes. Also, the smaller the content ratio of cobalt, the greater decrease in the output characteristics will be.
Also, there have been techniques to accomplish various objectives, such as mixing a boron compound such as boric acid with a lithium transition metal composite oxide, or placing a boron compound on the surface of lithium transition metal composite oxide.
JP 2001-257003A discloses a lithium secondary battery which has a positive electrode employing lithium manganate, in which a boron compound such as boron oxide, orthoboric acid, metabolic acid, or tetraboric acid, soluble in an electrolyte is contained in the positive electrode to suppress reaction between lithium manganate which has a spinel structure and hydrohalogenic acid, and thus improve cycle characteristics.
JP 2002-124262A discloses a technology in which a surface-treatment layer, which has good ion conductivity and includes a hydroxide, an oxyhydroxide, or the like of a coating element such as boron, is formed on a surface of lithium transition metal composite oxide, to increase discharge potential and to improve lifetime characteristics. In the coating that is specifically disclosed, a coating element dissolved in a solvent is deposited on a surface of lithium transition metal composite oxide, and then, the solvent is removed.
JP H10-079244A discloses a technology in which, in the process of forming an electrode made of a lithium transition metal composite oxide, boric acid or the like is added as an inorganic acid to prevent gelation of a paste for electrode. In JP H10-079244A, only lithium nickelate is disclosed as lithium transition metal composite oxide.
JP 2009-146739A discloses a technology in which on the surfaces of lithium transition metal composite oxide particles which contains nickel or cobalt as an essential component, a boric acid compound such as ammonium borate, lithium borate, or the like, is deposited, and is subjected to heat-treatment under an oxidation atmosphere to obtain high capacity of a secondary battery and to improve discharging efficiency and charging efficiency of the secondary battery. In JP 2009-146739A, only lithium nickelate in which a part of nickel is substituted with cobalt and aluminum is disclosed as a lithium transition metal composite oxide.
Nickel-cobalt-lithium manganate in which nickel, cobalt, and manganese are used as the transition metal, has a relatively good balance between cost and battery characteristics, but it is becoming increasingly difficult to meet demands in recent years on cycle characteristics and/or output characteristics in a specific compositional range.
Under these circumstances, the present invention has been made.